Under the Interim Standard IS-95-A (IS-95-A), which has been adopted by the Telecommunications Industry Association for implementing CDMA cellular telephones systems and personal communication systems (PCS), pages are sent from a base station to a mobile station over a forward channel referred to as a Paging Channel. The page informs the mobile station that a call has been placed to it.
IS-95-A provides for a slotted mode feature, which allows a mobile station to operate in a reduced power mode. That is, the Paging Channel is divided into 80 millisecond (ms) intervals called paging channel slots, and each mobile station operating in the slotted mode is assigned a specific slot in which they monitor the Paging Channel. The assigned slot is periodic-called a slot cycle. Because the mobile station only needs to monitor the Paging Channel during its assigned slot, at all other times of the slot cycle the mobile station can "sleep," that is, go into the reduced power mode, for example, by turning off its radio-frequency (RF) portion. To monitor the next periodic slot, the mobile station must "wake up" from its sleep in time to monitor the Paging Channel during the assigned slot.
Under IS-95-A, the time between successive paging channel slots is governed by the equation 2.sup.N .times.1.28 seconds, where N is the slot cycle index that is an integer from 0 to 7, inclusive. Thus, for a slot cycle index of 7, the time between slots is 163.84 seconds. A mobile station can request a particular slot cycle index, and the infrastructure can use the particular slot cycle index for timing the transmission of paging channel messages to the mobile station during the assigned slot.
If the slot cycle index is large, the mobile station will be asleep for proportionately large periods of time. Thus, the mobile station's power consumption can be reduced and standby time increased by requesting and using a large slot cycle index. A large slot cycle index, however, results in excessive call setup times. In the worst case, a call originating party would be forced to wait more than 2.5 minutes before the mobile station started to ring. In such cases, the origination party is likely to hang-up before the call is set up.
A user of a mobile station typically would want to receive the call, and would not want to inconvenience the originating party by requiring the originating party to wait a relatively long time for a call to set up. Consequently, there is a tradeoff between the user's desire to save battery power and increase standby times and the practical consideration of receiving calls. A need therefore exists for a wireless communication device and method that balances power savings and call setup time.